[poncho-mike]

While we're on the topic of oil pumps and Pontiac lubrication systems, I've always made some basic assumptions about Pontiac lubrication systems that may not be correct.

As I already mentioned, the Pontiac oil pump is a gear style positive displacement pump. The pressure coming out of the pump is regulated by a valve internal to the pump that limits the maximum oil pressure. I believe it may be possible to exceed that pressure under certain cases (such as a fully plugged filter or something blocking blocking the oil flow). At idle, the engine isn't pumping enough oil to exceed the oil pump pressure setting. As engine RPM increases the flow volume, pressure will rise to where the pressure is limited by the oil pump pressure valve . The oil leaving the pump goes into the oil filter adapter. There is a bypass valve in the oil filter adapter that will divert oil past the filter when pressure gets high enough due to high RPM or a restricted oil filter. At higher RPM, the oil from the oil pump bypasses the filter almost entirely. I think Pontiac engineering did this because they knew some car owners would let their oil filters get dirty, and they felt it safer to bypass the filter than to let the engine starve for oil.

What I don't know is how the bypass pressure setting in the oil filter adapter compares to the oil pump pressure setting. I always assumed that a standard production engine with a 45 psi oil pump was paired with an oil filter adapter that was set to bypass at a pressure slightly higher than the pump pressure. I also assume that an engine with a 60 psi pump has a different oil filter adapter than an engine with a 45 psi pump. What that meant to me was that when I rebuilt an engine and installed a 60 psi pump, I would replace the stock oil filter adapter with one from an engine that came from the factory with a 60 psi pump (Ram III, 70 455HO, etc).

The implication is this: If you put a 60 psi pump into an engine that originally came with a 45 psi oil pump, the pressure of the oil coming out of the oil pump might be higher than the pressure setting of the bypass valve, so you would be constantly bypassing the filter at anything above idle.

The alternative to that is that Pontiac engineering set the bypass pressure in the oil filter adapter high enough that it would work with a 45 or a 60 psi oil pump. That means there would be no difference between the oil filter adapter for an engine with a 45 psi pump vs a 60 psi pump.

Does anyone on this board know the answer to this question?

[Formulajones]

That's probably going to get into the discussion of blocking the bypass all together and the pros and cons of that.

[poncho-mike]

Yeah, I know.

I just wanted to know if I really needed to change the oil filter adapter when upgrading oil pumps.

I've asked that question before (not necessarily on this forum), and never got a answer I felt comfortable with. I tried to figure out if the part number for the oil filter adapter was different for a standard 455 vs a 455HO, but was never able to find the answer. I'm hoping someone here knows.

[1971455HO]

Thanks Mike & Formulajones for taking time to explain to me & maybe other novices here how it actually works. I did a bunch of reading yesterday online about those who intentionally block off their bypass to insure all oil is filtered. I know what can happen at wide open throttle, but I have no comment. I also read a post concerning bypass blocking from a very experienced Pontiac engine builder that said, wrong,wrong,wrong. Again I have no comment. I know I'm not going to. I try not to ask too many things on here and be a pest, but sometimes I have to if I can't find in the previous post searches. Oil pressure was one of those subjects I couldn't seem to find much on. The more I learn, more I realize how little I know. Thanks for the education gentlemen.

[poncho-mike]

I wouldn’t worry about asking a question. Most of the people on here are good people and will try to give you an answer in layman’s terms. I ask questions all the time, in fact I’m a little disappointed nobody has chimed in and commented on if the oil filter adapters are different for standard vs high performance engines.

For the average street car, it doesn’t make sense to block the bypass function in the oil filter adapter. There is little to gain, and much to lose.

One thing that has been briefly mentioned on this thread is that it the oil pressure can be different depending on where you measure it. Pressurized oil that flows to the main and rod bearings runs out the sides of the crank journals and returns to the pan. There are oil passages that direct oil to the camshaft bearings, and other oil passages that feed oil to the lifters, which in turn feed oil to the rocker arms and valves. If there is excessive clearance in your main bearings, rod bearings, or in the camshaft bearings, you could be getting insufficient oil to the top end of your engine.

There are a couple of things modifications I make on all of the engines that I have built. There may be some people on the board that will think these modifications don’t help that much, but I’ll throw them out for consideration.

I always remove the lifter galley plugs on the front surface of the block, behind the timing chain. To properly clean a block, you should remove the threaded plugs at the rear of the block and knock out the pressed in galley plugs at the front of the block. The machine shop then should run a rod through the oil passages to insure they are clean and remove any crud that has accumulated there. I then tap the two holes behind the timing chain and install threaded plugs to replace the pressed in plugs. I don’t tap the hole all of the way through the block, because you have to be careful that you don’t block the oil holes feeding the front lifters on the right and left banks. I also use threadlocker on these plugs. I think the SD455 blocks came from the factory with threaded galley plugs on front, all others were pressed in and staked.

The second thing I do is drill a hole in the galley plug behind the distributor gear. At the top of your engine, there is a galley plug located behind a freeze plug on the back of the block (behind the bell housing). If you drill a small hole in that plug before re-installing, it will spray oil on the distributor gear. H-O Specialties used to sell a kit containing a galley plug with a small hole drilled in it years ago. The purpose of this modification is to insure the distributor gear is adequately lubricated. Sometimes a machine shop will accidentally leave this plug out. When that happens, one whole bank of lifters will clatter.

The third thing is optional. There is a galley plug at the top of the block, near where the distributor in installed. If you want to know what the oil pressure is at the top of your engine (which may be different than what you read at the oil filter adapter), you can install a mechanical gauge in that that galley plug hole. The gauge can be installed temporarily for troubleshooting, or permanently if keeping the car stock isn’t a concern.

In another thread, I talked about how I made an engine stand to run in engines using a subframe out of a Trans Am I junked. I always monitor oil pressure at the oil filter adapter and near the distributor during run-in.

[77 Canamman]

1970-1979 350-455 engines all used 6437605 oil filter housing. None other was listed.

[1971455HO]

Originally Posted by 77 Canamman

1970-1979 350-455 engines all used 6437605 oil filter housing. None other was listed.

Thanks 77 Canamman.

So the 350 - 455 engines all got the same oil filter assembly (6437605) from 1970 to 1979 regardless of which psi oil pump. That eliminates the question of were there different by-pass valves installed for engines with 40psi, 60psi, or 80psi pumps installed.

This was a good article for guys like me that need to ask questions about oil systems: http://www.pontiacdiy.com/pontiac-v-...-system-guide/.

I understand how the oil filter bypass works now...its differential pressure. With the filter collecting contaminates & carbon to the point where oil flow has become restricted at higher RPM's resulting in a pressure drop, the higher pressure oil from the pump forces the spring loaded ball off it seat and opens the bypass as needed. I'm guessing the bypass opens every time the engine goes full throttle to insure continuous oil flow then closes when back to normal operating rpm.
Thanks Pontiac Engineers.

[rexs73gto]

Yes Pontiac did stop using the 80 lbs pump in the 74 model because the same thing that prompted them to restyle the dipstick for the 67 model cars some were running the cars sometimes a qt low or more & the good pump would suck all the oil up top & the crank being bigger were being starved. So rather then telling the cust's to put 6 qts in the oil pan it was easier to change the pump to 60 lbs & that cured a lot of the problem of oil starvation in the big journal cranks. But the 80 lbs pump is still the better pump as they work better & better designed for Pontiac engines. I run 6 qt with a full filter in all my cars & never have a problem. But again Pontiac was on an economy kick along with all of GM so the cust. wouldn't have to spend that extra on the extra qt. of oil to help cut down on maintenance costs. That way it would look as GM cars were lower in the maintenance cost vs the foreign car which were making big in roads in to the US. But as far as other concerns with the 80 lbs pump there weren't any more with it then the 60 lbs pumps. But I have to say that as mentioned before my engine thats in my 73 GTO right now has the M54F 80 lbs pump & cold pressure is right at 80 lbs, & warm idle is at 70 lbs. It goes up to 80 lbs when I hit the gas & if it got to 40 lbs at warm idle I'd be pulling it apart as there would be a problem somewhere. All of my engines have always had good oil pressure at idle & again if it went down by 1/2 I'd know there was a problem with it. While I was still working (GM service mgr.) we had some on these new engines come in & if the oil pressure was that low we would take them down & find the problem, even thou chevy said it was ok most cust. will NOT except that low of oil pressure on an new car or truck engine, & we always found a problem with them when they had that low of pressure. I know if it was my engine I'd be taking it apart to find your problem before it get to be a bigger one & cost you an engine.

[poncho-mike]

Originally Posted by 77 Canamman

1970-1979 350-455 engines all used 6437605 oil filter housing. None other was listed.

Thanks, that solves that question.

As far as I know, all Pontiac V8 motors from the late 60s thru the late 70s were intended to use 6 quarts of oil. I just checked the owners manual for my 1973 Formula and my 1975 Formula, and the capacities section states 6 quarts of oil when the filter is replaced.

I also have experienced fluctuating oil pressure at internet speeds on cars with 3.42 and 3.55 rear ends. Any time I was taking a car on the interstate, I would check the oil level, top it off, and if I were going on a long trip, I would add an extra quart.

I don't think you need anything greater than 60 psi oil pressure on the street.